2OO THE CHICAGO ACADEMY OF SCIENCES. 



ing abruptly downward laterally to the margins, with six strong 

 pleural ribs whose extremities are slightly produced, giving to 

 the pygidium slightly serrate lateral margins. 



The dimensions of the best preserved cranidium which has 

 been observed are: length along median line 6 mm., width be- 

 tween eyes 9.5 mm., width at posterior margin 13 mm. The 

 dimensions of a pygidium are: length 5 mm., width 6 mm. 



Remarks. This is a small species and is known only from 

 more or less fragmentary cranidia and pygidia. These two 

 portions of the body occur together at the only locality where 

 the species has been observed, and since they are associated 

 with no other members of the genus, it seems safe to consider 

 them as portions of a single species. The species is 'especially 

 characterized by the narrow, flattened anterior marginal border 

 with its symmetrically arranged row of tubercles. The pygidium 

 may be distinguished by reason of its proportionately greater 

 width than is usual in the genus. The condition of preservation 

 of all the specimens examined leaves it uncertain as to the pres- 

 ence of genal spines ; these seem to be absent from the specimens 

 studied but additional material may show that they were pres- 

 ent. 



Locality. Near Joliet. 



Family 8. CALYMENIDAE Brongniart. 



"Cephalon somewhat wider than long. Fixed cheeks large; 

 genal angles rounded or produced into spines. Glabella narrow- 

 ing anteriorly. Free cheeks long, separate, usually with a free 

 plate between the anterior extremities. Sutures extending from 

 just in front of the genal angles, converging anteriorly, and 

 cutting the margins separately. Eyes small, facets numerous, 

 visual surface seldom preserved. Thorax of thirteen segments, 

 with grooved pleura. Pygidium of from six to fourteen seg- 

 ments; axis tapering." Beecher, Zittel-Eastman Text Book of 

 Paleontology, p. 634. 



Genus 15. CALYMENE Brongniart, 1822. 



Complete body sub-oval in outline, possessing the power 

 of complete enrollment; cephalon sub-crescentiform with thick- 

 ened margin, genal angles usually rounded; glabella strongly 

 convex, narrowed in front, with three pairs of deep lateral fur- 

 rows; the occipital segment well defined; posterior limbs of the 

 facial sutures originating just in front of the genal angles; free 

 cheeks elongate, separate, usually with a free plate between 



